In an apparatus employing an electrophotographic technique such as a copying machine, a printer, and a facsimile, a two-component developer including a toner and a carrier for developing an electrostatic latent image on the surface of a photoconductive member is stored in a developing device. The developing device supplies the toner to the surface of the photoconductive member.
In a dry-type two-component developer, the toner is consumed by development of a latent image but the carrier remains in the developing device. A resin coat material on the surface of the carrier peels or a toner component adheres to the surface. Such a carrier deteriorates charging performance of the developer and causes deterioration in an image characteristic.
There is known a configuration for, in order to gradually replace a carrier, storing a developer obtained by mixing a toner and a small amount of the carrier in a developer supply container and supplying the carrier to a developing device together with the toner.
Among image forming apparatuses employing such a configuration, there is an image forming apparatus in which, in order to automatically perform replacement of the two-component developer, a developer overflow section at predetermined height is provided on a downstream side of the developer to be agitated and moved.
Usually, the two-component developer includes a toner and a carrier. When the number of sheets to be printed increases, fluidity of the developer changes and the developer is not smoothly discharged from the developer overflow section. Therefore, the developer is held up more than necessary and is not discharged unless the quantity of the developer substantially increases. As a result, a spill of the developer and development unevenness occur.
Therefore, the present invention provides a developing system and a developing method in which, even if the number of printed sheets increases, the fluidity of a developer does not substantially fall and a spill of the developer and density unevenness do not occur for a relatively long period.